linux-kernel - Re: [PATCH] memcg: add hierarchical effective limits for v2

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Message-ID: <mshcu3puv5zjsnendao73nxnvb2yiprml7aqgndc37d7k4f2em@vqq2l6dj7pxh>
Date: Thu, 6 Feb 2025 16:57:39 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org, cgroups@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH] memcg: add hierarchical effective limits for v2

Hello Shakeel.

On Wed, Feb 05, 2025 at 02:20:29PM -0800, Shakeel Butt <shakeel.butt@...ux.dev> wrote:
> Memcg-v1 exposes hierarchical_[memory|memsw]_limit counters in its
> memory.stat file which applications can use to get their effective limit
> which is the minimum of limits of itself and all of its ancestors.

I was fan of equal idea too [1]. The referenced series also tackles
change notifications (to make this complete for apps that really want to
scale based on the actual limit). I ceased to like it when I realized
there can be hierarchies when the effective value cannot be effectively
:) determined [2].

> This is pretty useful in environments where cgroup namespace is used
> and the application does not have access to the full view of the
> cgroup hierarchy. Let's expose effective limits for memcg v2 as well.

Also, the case for this exposition was never strongly built.
Why isn't PSI enough in your case?

Thanks,
Michal

[1] https://lore.kernel.org/r/20240606152232.20253-1-mkoutny@suse.com
[2] https://lore.kernel.org/r/7chi6d2sdhwdsfihoxqmtmi4lduea3dsgc7xorvonugkm4qz2j@gehs4slutmtg

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